A read channel integrated circuit (IC) is one of the core electronic components in a modern magnetic recording system, such as a hard disk drive. A read channel converts and encodes data to enable the heads to write data to the disk drive and then read back the data accurately. The disks in a drive typically have many tracks on them. Each track typically consists of mostly user or “read” data sectors, as well as control or “servo” data sectors embedded between the read sectors. The servo sectors help to position the magnetic recording head on a track so that the information stored in the read sectors is retrieved properly.
The servo data format includes a preamble pattern that is used to estimate the timing and gain information. Gain error estimation is currently performed in two steps. Initially, an initial gain error estimate is obtained using, for example, a Zero Gain Start (ZGS) technique based on a Discrete Fourier Transform (DFT) technique. The initial gain error estimate is then followed by another gain error estimation using, for example, a more precise Zero Forcing (ZF) algorithm. While this conventional technique is accurate, a number of preamble cycles are consumed, which impairs the format efficiency.
Thus, a need exists for improved techniques for gain error estimation in magnetic recording systems, such as hard disk drives.